The present invention concerns an arrangement for melting at least one solid precursor product for polymer production, and an apparatus for the production of a polymer molding comprising at least two different solid precursor products.
The invention is concerned with the topic of melting polymers, prepolymers or polymer precursors for subsequently reactive processing.
A wide range of different approaches can be supposed as known as the state of the art for melting solid precursor products in the form of reactive components and subsequent reactive processing. In the case of lactams, in particular c-caprolactams and subsequent polymerization to give polyamide 6 that is to be viewed primarily in the context of the following processing steps.
The processing of additivated caprolactam-based melts in reactive installations in the context of the resin injection process is known, in which melting or heating of the precursor products is effected in stirred, generally pressurized or evacuated, vessels. In that case, the components are circulated by way of pump or dual-piston systems. A plurality of reactive components are combined in a mixing element from which the reactive mixture is discharged into an open or closed mold. By way of example in that respect, attention is directed to DE 1 299 885 and DE 600 31 851 T2.
The discontinuous production of components or blocks on a polyamide basis is further known in the context of production of cast polyamide. In that case, the non-additivated monomers are usually melted and stored above melting temperature with the exclusion of moisture in suitably sized containers and are only additivated prior to use.
A further possible way of melting and subsequently processing reactive components, in particular for ε-caprolactam or laurolactam, as described in EP 2 572 851 A1, represents thrust screw plasticization, wherein the melting and injection operations in respect of the respective reactive component are performed in a functional unit.
Particularly for low-viscosity substances it is possible to operate in that context with seals based on polymers (EP 2 454 075 B1). In that respect, the heating and melting process is based on both a shearing action and also thermodiffusion.
Comparable piston-based systems are known, primarily for non-reactive systems, in which the substances to be melted are pressed under pressurization conditions by way of the most widely varying kinds of shearing and mixing portions and thus the energy input is maximized in relation to high-viscosity masses. As an example here, reference may be directed to DE 10 2006 038 804 B3.
As already stated in DE 1 942 992, piston-based systems are further known, in which the preheated reactive components are already mixed in a single piston and discharged only after initiation of the reaction in order to simplify the sealing effect during the displacement of the injection piston, due to the higher viscosity of the reactive mixture. Particularly for very bulky components like, for example, rotor blades of wind turbine rotors vacuum infusion with preferably thermosetting resin systems has become established, corresponding approaches based on low-viscosity precursor substances of thermoplastic polymers like ε-caprolactam were described in Composites: Part A 38 (2007) 666-681.
In current reactive installations for the processing of reactive components liquefied, low-viscosity, additivated components are continuously heated and circulated under high pressure, this entailing a considerable energy consumption. In addition, the components are subjected to a considerable residence time divergence due to the periodic removal of individual aliquots for component production and the feed of new components, which can have a detrimental effect on the stability of the individual components or additives. In particular, the additives used for the production of polyamides by anionic polymerization can be damaged or deactivated by premature autopolymerization. In particular, a substantially larger melt volume is heated throughout and kept above melting temperature than is necessary at the respective moment in time for processing.
In the case of thrust screw-based systems which can be used for melting and metering corresponding reactive components, there is a negligible residence time divergence unlike the situation when using concepts based on melt storage means. By virtue of the implementation of the melting and injection operation in one functional unit, however, the required back-flow blocking means is to be viewed as a weak point, which prevents melted material being urged back into the melting region when there is a build-up of pressure and in the injection process. Particularly in the case of low-viscosity systems, durable sealing and reproducibility is highly problematic in that case. The energy input due to a shearing action is also negligible, in the case of low-viscosity systems.
The joint injection of the reactive components after previous mixing in an injection piston is to be viewed as a disadvantage in particular in regard to reproducibility and possible deposits in the injection piston used. In addition, that principle cannot be economically applied a priori in the case of more complicated and expensive shape geometries and with longer flow paths as the situation would involve hardening prior to complete filling of the component cavity. In addition, the injection of a mixture which is already of higher viscosity means that the infiltration of textile reinforcing elements like, for example, a fiber semi-finished product or preform is made seriously more difficult.